1. Field of the Invention
The present invention is directed to the field of surface cleaning and etching of wafers such as silicon substrates and, more particularly, to an improved apparatus for enhancing the process of treating a plurality of semiconductor wafers.
2. Description Relative to the Prior Art
The use of ultrasonic energy to enhance the cleaning action of solutions used on semiconductor wafers is well established and has been described in U.S. Pat. Nos. 3,198,489, 3,240,963, 3,893,869 and 4,401,131. Ultrasonic agitation has also been used to enhance the etching action of etching solutions on similar semiconductor wafers. Such cleaning and etching processes are now commonly used in the production of semiconductor devices and have used transducers operating at both intermediate frequencies, i.e., 20-50 KHz, and, more recently, frequencies of 0.2 to 5.0 MHz. As noted in U.S. Pat. No. 4,602,184, the use of the high frequency, or megasonic, agitation of the solutions has resulted in improved cleaning and etching, paticularly on wafers with very small, micron-sized components or elements thereon. Further, the use of such high frequency agitation has resulted in a gentler cleaning action on the wafers than that obtained with intermediate frequency agitation. As a result, damage to the micro-sized components during the etching and cleaning operations during the production of the semiconductor wafers has been significantly reduced with the use of high frequency agitation. The productivity of the semiconductor production system has thus been improved due to the reduction in damage to the elements on the semiconductor wafers.
Various attempts have been made to provide high frequency agitation to tank-type cleaning and etching baths with megasonic-frequency-generating transducers mounted to the inner surface of the tank walls. Some of these arrangements have employed apparatus to move the wafer-containing cassettes through the energy beam created by the transducers to assure that all portions of the wafer surfaces have been treated by the energy beam to insure that they have been adequately treated. Such arrangements have been found to be less than satisfactory due to the fact that the tank must be sufficiently large to permit the movement of the cassettes past the transducers, requiring larger tanks and more space in the clean rooms normally used for such processes, to provide space necessary for such cassette movement. Moreover, the larger tank volume requires a significantly larger volume of cleaning or etching fluid to fill the tank. Further, it has been found that the movement of the cassette containing the semiconductor wafers has caused edge damage to the wafers because of the motion of the cassettes and the wafers through the cleaning or etching bath. Still further, it has been found that due to the high power operation of the transducers, they must be replaced regularly. This has proven to be a time consuming and costly task with cleaning systems of the prior art, often requiring the emptying of the tank of the highly reactive fluid therein.
Thus, a megasonic cleaning and etching device obviating the foregoing problems, providing higher wafer yield with less damage to the wafers, permitting smaller space requirements and less fluid use, as well as easier transducer maintenance, will achieve widespread acceptance in the semiconductor manufacturing industry.